1. Field of the Invention
The present invention relates to a packet communication node apparatus, and more particularly to a packet communication node apparatus whose hardware functions are made extensible by the addition of a functional module or modules.
2. Description of the Related Art
The main function of communication node apparatuses, such as routers, constituting a packet communication network is to relay or transfer packets between network lines. If such a communication node apparatus can have one of the communication service functions which have so far been performed by a server or a data processing device connected to the communication network, it will provide an advantage that responses to user terminals are quickened and traffic on the network is reduced. In this case, it is preferable for any communication service function added to the communication node apparatus to be flexibly extensible to meet possible new needs of users and the market.
Known packet node apparatuses permitting extension of communication service functions include, for instance, what is proposed in the Japanese Unexamined Patent Application No. 2002-281072 (US 2002/0150088 A1: Patent Reference 1). It relates to an inter-network device comprising a plurality of routing modules connected to one another by a host bus and a line control module coupled to each routing module by a subordinate bus, and proposes to replace one of the line control modules accommodating network lines with a functional extension module, transfer IP packets whose header information satisfies conditions prescribed in a detection condition table in advance, out of the IP packets transferred from the line control modules to the routing modules, via the host bus to the routing module accommodating the functional extension module, and having that routing module supply received packets to the functional extension module thereby to cause the functional extension module to process a service, such as encrypting the received packets, for instance.
The packet node apparatus described in the Patent Reference 1 has an advantage of scalable realizing functional extension of the node apparatus because a new service processing function can be added to the node apparatus by partly altering the functions of the routing modules and replacing part of the line control modules with the functional extension module.
However, since each routing module which has to perform high speed processing of received packets has no capability for payload analysis of received packets, the detection condition table is obliged to select the received packets to be transferred to the functional extension module merely on the basis of header information extractable from the packet header, such as the destination IP address, the source IP address and the TCP port number. Therefore, it is difficult for a system which controls packet transfers to a functional extension module by a routing module coupled to a line control module as proposed in Patent Reference 1 to accomplish highly precise allocation of packets, which presupposes analysis of payloads, and is accordingly limited in the variety of functional extension modules connectable to a node apparatus.